However, one of the other students in my project group has a very different understanding of EIRP than I have. He is fully convinced that the EIRP-values in the link budgets are given per antenna cluster, not per antenna.

(Most BTS-installations (at least around here) are made with tree antennas, each covering 120 degrees. This means that each antenna cluster (consisting of three antennas) cover 360 degrees.)

In all of the antenna installations I have made (albeit radio links, not BTS) EIRP was always understood to be calculated/declared per antenna, not per system or per antenna cluster.

I am pretty sure that my understanding of the EIRP concept is correct - that EIRP always is per antenna, but I cannot (despite a couple of days searching) find any sources (online or in the library) which clearly settles the issue.

The professor teaching the course is on holiday, so I cannot get any help there.

Any help is greatly appreciated! Especially a reference to some authoritative material which clearly settles the issue.

I don't agree. Effective Isotropic Radiated Power needs to be istropic, that is must be the same in all directions at a fixed distance from the radiator. If we had a gain versus azimuth plot for a tree antenna we could see if the isotropic radiator correctly models such an antenna. I believe that the goal of the tree-antenna is to do that, I'm just not sure how pronounced the lobes are.

I don't agree. Effective Isotropic Radiated Power needs to be istropic, that is must be the same in all directions at a fixed distance from the radiator. If we had a gain versus azimuth plot for a tree antenna we could see if the isotropic radiator correctly models such an antenna. I believe that the goal of the tree-antenna is to do that, I'm just not sure how pronounced the lobes are.

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Thank you for your reply!

Gain/azimuth-plots have not been mentioned in the class in relation to the assignment. I agree that the modelling would be vastly more realistic if the values were taken from actual antenna specifications with gain/azimuth-plots instead of generic textbook examples.

Both in Balanis "Antenna Theory" and in the books referenced above EIRP is calculated as transmitter power * antenna gain. Do you mean that the available transmitter power (44.5-46 dBm) actually is shared between the three 120 degree (18dBi gain) antennas in the antenna cluster?

No not exactly. I think what is happening is that the three antennas together, with some sleight of hand called a phasing harness, match the transmission line and the transmitter output impedance of 50 Ohms. You would have to know exactly how they were connected to be sure.

No not exactly. I think what is happening is that the three antennas together, with some sleight of hand called a phasing harness, match the transmission line and the transmitter output impedance of 50 Ohms. You would have to know exactly how they were connected to be sure.

VHF operators use the phasing harness on stacked yagis all the time.

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Thank You!

I didn't know phasing harnesses could be used with mobile telephony systems!